All modern applications generally fetch data from remote services (e.g. REST or SOAP). The data is mostly either XML or JSON format. Gson helps applications in Java-JSON serialization and deserialization automatically (as well as manually, if needed, using simple
Gson can work with arbitrary Java objects including pre-existing objects that we do not have source-code of.
The best benefit of Gson is that it does not make mandatory to add annotations into java classes, until we are doing something very specific for certain member fields.
Note that the
Gson instance does not maintain any state while invoking JSON operations. So, you are free to reuse the same object for multiple JSON serialization and deserialization operations.
In this Gson tutorial, we will learn to use it effectively in our applications.
1. Gson Fundamentals
In this first part, we will get to know Google Gson library and its basic mapping functionality.
- Installation – Learn to include gson dependency in the java applications using build tools like maven, gradle or simple jar file.
- Simple Serialization and deserialization – Learn to use GSON to serialize simple Java Object into the JSON representation and to deserialize the JSON string to an equivalent Java object.
- Compact Vs. Pretty Printing for JSON Output Format – The default JSON output that is provided by Gson is a compact JSON format. Use the Pretty Print feature to format the JSON for reading purpose.
- Mapping of Arrays and Lists of Objects – Learn to use Google GSON library to deserialize or parse JSON, containing json array, to java array or java list objects.
- Mapping of Sets – Learn to use Google GSON library to deserialize or parse JSON to Set (e.g. HashSet) in java.
- Mapping of Maps – Learn to serialize HashMap using Google Gson library. Also learn to deserialize JSON string to HashMap containing custom Objects using Gson such that field values are copied into appropriate generic types.
2. Advance Usages
Basic examples in first part are good enough for default usecases. We may need to customize the behavior of Gson to support specific requirements. Learn how to do this.
- Customize Gson object with GsonBuilder – For simple usecases, using
'Gson gson = new Gson();'is enough. Learn to use GsonBuilder to create a new Gson instance with the customized configuration.
- Serialize Null Values – By default, Gson omit the null values. Learn to include null values during serialization and deserialization.
- Versioning Support – Multiple versions of the same object can be maintained by using @Since annotation. Gson will ignore Gson any field/object that is greater than the configured version number.
- Custom field names using @SerializedName – Learn to use Google GSON library to serialize Java Objects into their JSON representation and to deserialize a JSON string to an equivalent Java object.
- Excluding Fields From Serialization and Deserialization – Gson supports numerous mechanisms for excluding top-level classes, fields and field types. Learn how to use them.
- JsonReader – Streaming JSON parser – Learn to read a JSON string or file as a stream of JSON tokens.
- JsonParser, JsonElement and JsonObject – Learn to parse a JSON string or stream into a tree structure of Java objects into JsonElement.
- Custom Serialization and Deserialization – Learn to parse a JSON string or stream into a tree structure of Java objects into JsonElement.
- Gson Tutorial – Recap – Let’s recap most important topics we have learned so far.
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